1. Field of the Invention
The present invention relates to an electric actuator for moving a displacement member by transmitting a driving force of a driving section to the displacement member via a driving force-transmitting belt.
2. Description of the Related Art
An electric actuator, which displaces a slider in order to transport a workpiece or the like, by driving a belt by means of a rotary driving force of a rotary driving source such as a motor, has been hitherto widely used as a workpiece-transporting apparatus.
In recent years, an electric actuator having a thin type of structure has been developed, in which a height dimension of the electric actuator is suppressed, taking into account demands of the installation space as well as the environment of use of the electric actuator.
Such an electric actuator comprises, for example, a guide rail disposed in an axial direction along a central portion of a housing, and a guide block, which is slidably displaceable along the guide rail, wherein a slide block is connected to an upper portion of the guide block. Further, a transmitting belt moves orbitally inside the housing, such that the transmitting belt surrounds the outer sides of the guide rail, wherein the transmitting belt is connected to the slide block. When the transmitting belt is driven by a driving source, the slide block is displaced along the guide rail.
In a conventional technique disclosed in Japanese Laid-Open Patent Publication No. 8-226514, a guide rail and a transmitting belt are arranged substantially in parallel in the horizontal direction inside a housing, with the intention of miniaturizing a height dimension of the electric actuator. On the other hand, the widthwise dimension of the housing is inevitably increased, and the electric actuator consequently has a large size in the widthwise direction, since the transmitting belt is arranged so as to surround the outer sides of the guide rail.
In another viewpoint, it may be conceived that the widthwise dimension of the guide rail should be made large in size in order to facilitate rectilinear movement performance when the guide block and the slide block are displaced. However, in this case, the housing inevitably becomes large in size, because the transmitting belt is arranged on the outer sides of the guide rail. Thus, it is difficult to obtain a desired widthwise dimension of the guide rail while the widthwise dimension of the electric actuator itself is suppressed. Therefore, for example, when an external force is applied in the moment direction with respect to the slide block, the slide block cannot be smoothly displaced along the housing in some situations.